Various techniques may be used to print features such as patterns that define integrated circuits on semiconductor wafers. In general, electromagnetic wave emissions from a source are directed to expose selected locations on a substrate while leaving other locations unexposed. Example emissions include visible light, ultraviolet (UV) and extreme ultraviolet (EUV) radiation, and X-rays. Example approaches to directing these emissions toward selected locations include selective attenuation (e.g., using binary photomasks), interference (e.g., using phase shifting masks), reflection (e.g., using EUV reflective optical elements), and beam steering.
Regardless of the approach used to direct such emissions, diffraction orders that scale with the wavelength of the emission may blur the boundary between directly exposed locations to which the emission is directed and other locations to which the emission is not directed. Such blurring makes the printing of features with dimensions in the vicinity of the wavelength more difficult. For example, when features are proximal, the features may not resolve due to diffractive exposure of the intervening space.
When adjacent contacts in a contact pair are not resolved, they tend to behave as a single contact. For example, forming a contact with a first contact of an unresolved pair generally results in inadvertent shorting with the second contact.
Like reference symbols in the various drawings indicate like elements.